Accretion definition, an increase by natural growth or by gradual external addition; growth in size or extent. See more.
Alveoli are tiny sacs within our lungs that allow oxygen and carbon dioxide to move between the lungs and bloodstream. Learn more about how they function and quiz your knowledge at the end.
Gas exchange. We need to get oxygen from the air into the blood, and we need to remove waste carbon dioxide from the blood into the air. Moving gases like this is called gas exchange. The alveoli are adapted to make gas exchange in lungs happen easily and efficiently.Here are some features of the alveoli that allow this:they give the lungs a really big surface area. they have moist, thin walls (just one cell thick). they have a lot of tiny blood vessels called capillaries.he alveoli are adapted to make gas exchange in lungs happen easily and efficiently. Here are some features of the alveoli that allow this: they give the lungs a really big surface area. they have moist, thin walls (just one cell thick). they have a lot of tiny blood vessels called capillaries.